1. Technical Field
The present invention relates to a surface acoustic wave resonator using a piezoelectric substrate, a surface acoustic wave oscillator, and a surface acoustic wave module device.
2. Related Art
Surface acoustic wave resonators using a surface acoustic wave (SAW) have been widely used as electronic apparatuses. In recent years, along with the popularization of portable apparatuses, it is required to downsize the surface acoustic wave resonators, which are used for the portable apparatuses. If the number of pairs of interdigital transducer (ITD) is reduced for downsizing the surface acoustic wave resonator, a decrease in a Q value or an increase in a crystal impedance (CI) value is caused. Thereby, characteristics of the surface acoustic wave resonator cannot be substantially obtained. The decrease in the Q value blocks excitation of a stable surface acoustic wave while the increase in the CI value causes an increase in power consumption in an oscillation circuit. As a countermeasure against these, for example, a technique for downsizing a surface acoustic wave resonator is disclosed in JP-A-2004-194275. The surface acoustic wave resonator can be downsized by dividing the IDT into three regions and electrode fingers in each region of the IDT are formed at a fixed pitch which differs within 2%. As a result, the Q value is increased and the CI value is decreased, allowing the surface acoustic wave resonator to be downsized.
However, as characteristics of a surface acoustic wave resonator, the larger the Q value, the more excitation of a surface acoustic wave is stabilized. In addition, the smaller the CI value, the lower power consumption can be achieved. Thus, a surface acoustic wave is required that is downsized and whose characteristics are enhanced.